Numerous industrial processes require the use of gases which are considered dangerous because they are highly flammable, corrosive or toxic.
For example, excimer lasers require dangerous gases such as fluorine and hydrogen chloride for normal laser operation. These gases are a problem for the laser user because of their characteristics. In addition, excimer lasers suffer from a problem in regard to the inability of the operator to operate the laser with constant power output at a constant discharge voltage, while maintaining a good beam profile because of the inability to maintain a stable halogen concentration.
One method of handling dangerous gases of the type used for excimer lasers is by using dilute mixtures of the dangerous gas with a laser buffer gas, e.g. five percent or less halogen gas (e.g. fluorine or hydrogen chloride) in a buffer gas (e.g. helium, neon or mixtures thereof). This mixture is introduced into the laser with another rare gas component, e.g. argon, xenon or krypton. Using dilute mixtures of the dangerous gas and the buffer gas requires a high pressure cylinder (typically 1,000 to 2,000 psig) in order to provide enough halogen to operate the excimer laser for acceptable periods of time. Certain potential users of excimer lasers have decided not to use this type of equipment because of the necessity for handling dangerous gases which are susceptible to leakage when stored and delivered using conventional gas handling technology.
As the laser operates, fluorine is lost from the mixture and thus fluorine must be replenished. A common practice called "boosting", is a process, in which a small amount of the dilute fluorine/buffer gas mixture is added to the laser to make up for the depletion of fluorine that occurs during normal operation. This method can only be used for a given number of cycles after which the gas composition has been so altered the laser will not operate satisfactorily. The gas charge must then be vented and the laser re-charged with a new gas mixture, resulting in unwanted downtime and increased gas expenditures.
Recently a method has been developed as an alternative to use of high pressure gases by utilizing a gas generator. Undiluted fluorine gas is generated by heating a solid metal fluoride powder which is known to evolve fluorine when heated and is added to the laser by circulating the laser gas over or through the solid. This method overcomes the problem of buffer gas dilution but suffers from other aperational difficulties. Such a device must be operated at high temperatures, e.g. 250.degree.-300.degree. C., to generate sufficient quantities of fluorine thus causing safety and corrosion problems because of the handling of fluorine at high temperatures. Also dust from the metal fluoride powder is a problem since it must be prevented from entering the laser gas and fouling the laser optical system. In such a system when the metal fluoride is depleted of fluorine it must be regenerated with gaseous fluorine at high temperature and pressure which means the removal of the source from the system and returned to the supplier for regeneration. Experience has shown that because of the number of regenerations of a particular charge of metal fluoride required to have enough available fluorine, this may result in unacceptable costs associated with the fluorine generator.